Ag@BSA core/shell microspheres as an electrochemical interface for sensitive detection of urinary retinal-binding protein.

The level of urinary retinol-binding protein (RBP) can be estimated as a significant index of renal tubular injury. In this work, we used Ag@BSA microspheres as a sensing interface to cross-link RBP monoclonal antibody (RBP mAb) via glutaraldehyde for sensitive detection of RBP. The Ag@BSA microspheres covered on a Au electrode could provide a larger surface area and multifunctional substrate for the effective immobilization of RBP mAb, and the outside BSA layer acted as a biocompatible support to maintain the bioactivity and stability of immobilized immunogen. Electrochemical measurements containing electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) were employed to evaluate the analytical performance of the fabricated immunosensor and a higher detection sensitivity was obtained by DPV attributed to the excellent electrical conductivity of Ag@BSA which could enhance the peak current response. This immunosensor had a best detection limit (DL) of 18 ng mL(-1) and a linear response range between 50 and 4500 ng mL(-1). The proposed approach showed high specificity for RBP detection, acceptable reproducibility with an RSD of 5.6%, and good precision with the RSD of 4.5% and 6.3% at the RBP concentrations of 500 and 1500 ng mL(-1). Compared with the ELISA method by analyzing real urine samples from a patient, this immunosensor revealed acceptable accuracy with a relative deviation lower than 6.5%, indicating a potential alternative method for RBP detection in clinical diagnosis.